In the field of miniature electronic devices there are miniature components having conductive end terminations that require testing to assure the quality of the electronic capabilities. One type of contactor used to temporarily connect to the conductive ends of the electronic devices for the purpose of electrical measurements includes a contact roller, either standard size or micro size. Other types of contactors include sliding contact tips, sometimes referred to a blade, a disc or a wire tip. The various contactor module types can be used for testing the particular electronic components and are selected depending on the operating conditions such as: high contact pressure-high electrical power measurement; high contact pressure-low electrical power measurement; low contact pressure-high electrical power measurement; or low contact pressure-low electrical power measurement.
The various contact module types can be made of an electrically conductive metal material. The contact roller type is rotatable on an axis secured to a base plate or frame work of the testing machine via a spring support. The spring support may vary in length and include springs that continually bias or urge the support to the maximum length. Presently, the contact roller is preloaded to a constant spring force. As the test plate moves, the spring support urges the roller toward the path surface whereby the roller rolls on or at the same time presses on the surface of the test pad. As an electrical component moves to the test area via a test plate, the roller rolls off the path surface and on to the end of the electronic component to be tested. Once the roller is fully pressed into the component, the part is ready for testing. The downward force exerted by the roller on the component during testing is the same predetermined force exerted on the surface of the test path as the test plate moves. The required contact force to make a proper test measurement on an electronic component is about 50 grams. However, as the components to be processed get smaller, the resilience of the metal termination of the components diminishes to a point where the allowable contact load drops below the required load for stable testing. The maximum allowable force for the smaller electronic components during motion is only about 20 grams. Therefore, additional force placed on a moving electronic component can cause damage to the component.
Another procedure to eliminate damage to the electronic component includes activating the contact roller so that the roller does not touch the surface of the test plate or the electronic component while the test place is in motion. This procedure requires the contact roller to be retracted from the test plate and component while the test plate is in motion and then extended when the test plate stops and the component is in place for testing. In this procedure, the contact roller is actuated by a solenoid coil. When the solenoid coil is de-energized, the contact roller is in a raised position above the test plate. Once the test plate stops and an electronic component is in place at the test station for testing, the solenoid coil energizes and lowers the contact roller. The contact roller is preloaded to a 50 gram vertical force on the electronic component to allow for a stable testing environment. The disadvantage of this procedure is that the raising and lowering of the contact roller causes 5% to 13% decrease in productivity of the testing system.
Currently, the upper electrical contacts for electrical measurement of the miniature electronic component include a cantilever arm that will increase the contact force on the component as the deflection of the cantilever spring arm is increased. Multiple contacts are used at each test station, and the contacts are co-planarized in order to produce roughly the same contact force at a given deflection setting. Alternatively, compression springs are sometimes used to provide the contact or down-force. Additionally, flat spring fingers are sometimes used to produce the force needed. If it is desired to change the nominal force value, the spring force source must be changed out, or the position of the contactor must be changed with respect to the device under test in order to increase or decrease the compression of the spring force source in order to increase or decrease the force output. The spring force sources will also fatigue over time and require replacement.